Carbon brush assembly



April 1968 E. P. EATON, JR. ETAL 3,376,444

CARBON BRUSH ASSEMBLY Filed Sept. 15, 1965 2 Sheets-Sheet 2 Fm. 7 F7618INVENTOR 648 14744; B 04 |//0 United States Patent 3,376,444 CARBONBRUSH ASSEMBLY Edgar P. Eaton, Jr., Morristown, N.J., and David Elow,

New Rochelle, N.Y., assignors to Carbone Corporation, Boonton, N.J., acorporation of New Jersey, and Consolidated Spring Corp., Brooklyn,N.Y., a corporation of New York Filed Sept. 13, 1965, Ser. No. 486,836 2Claims. (Cl. 310-249) ABSTRACT OF THE DISCLOSURE A carbon brush assemblyfor electrical motors in which the end of the brush is formed with acavity into which a portion of a helical electric contact spring isreceived. The end of the spring is shaped to conform to the shape of thecavity to provide good electrical contacts therebetween under alloperating conditions.

This invention relates to a carbon brush assembly for small and mediumpower electric motors. It has particular reference to a low resistancecoupling between a helical spring and a carbon block so that the usualflexible wire shunt is unnecessary.

The use of carbon brushes to form a sliding electrical connection iswell known. They are used on commutators and slip rings attached'to arotor in many types of electrical motors and converters. Since thecommutator or slip ring rotates and cannot be perfectly round, the mostsuitable device for maintaining constant electrical contact is a springof some type. Helical springs are universally used on small motorsbecause they are compact and may be installed within a brush holder.

Springs are generally made of steel which is not a good conductor ofelectricity. If they are the only means for conveying the current fromthe brush to the outside circuit they are liable to overheat and losetheir temper. For this reason, most of the brushes which carry currentsof one ampere or more are now fitted with a flexible copper wire shuntwhich carries all of the current.

New types of springs have recently been introduced which have therequired elasticity and, in addition, a low resistance. They are alloysof Phosphor bronze, beryllium copper, and other mixtures, one of whichis commercially known as Cortem. Springs made of these materials can beused to furnish the resilient force needed by commutator brushes and tocarry currents up to and including ten amperes. It has been found thatin such applications, other problems are present, one of which is thenecessity of making a good electrical contact between the end of thespring and the carbon brush. This problem is further complicated by thefact that when a helical spring is compressed, the turns expand slightlyand if the turns are fitted around a cylindrical extension of the brush,compressing the spring causes a reduction of the contact force andprobable arcing. The present invention solves this problem by placingthe lower end of the helical spring within a cavity formed in the upperend of the brush. Then when the spring is compressed, the electricalcontact is maintained.

As used throughout the specification and claims, the term cylindricalrevolving conductor, refers to all classes of commutators and slip ringsused on motor rotors. It also refers to revolving contact segments andrings which are used to make and break current to contact brushes.

An object of the present invention is to provide an improved carbonbrush assembly which avoids one or more of the disadvantages andlimitations of prior art assemblies.

3,376,444 Patented Apr. 2, 1968 Another object of the present inventionis to provide a low resistance contact between a spring and a commutatorbrush for carrying current from a commutator to other parts of a motoror external circuit.

Another object of the present invention is to eliminate the flexiblewire shunt on the smaller sizes of motors and in other applicationswhere current does not exceed ten amperes.

A further object of the present invention is to reduce the cost of brushassemblies.

Still another object of the present invention is to simplify theoperation of assembling the motor parts and to aid in repair work.

Another object of the present invention is to eliminate other types ofbrush parts that take up space and might be dangerous if contact is madewith a commutator segment or a slip ring.

, A still further object of the present invention is to increase thesliding stability of the brush in its holder and provide extra wear byincreasing the length of the brush faces in contact with the holder.

The invention comprises a carbon brush slidably mounted in a brushholder. The brush is formed with a cavity at one end for receiving oneterminal of a helical spring; The helical spring has its other endabutting a cap on the holder and resiliently urges the brush against arevolving commutator or a sip ring. The brush cavity may be cylindricalor conical or a transverse slot.

The invention consists of the construction, combination and arrangementof parts, as herein illustrated, described and claimed.

In the accompanying drawings, forming a part hereof, is illustratedseveral forms of embodiment of the invention, in which drawings similarreference characters designate corresponding parts, and in which:

FIGURE 1 is a cross-sectional view, taken generally along a centralplane, of a prior art brush holder showing the wire shunt.

FIGURE 2 is a cross-sectional View of the brush assembly shown in FIGURE1 and is taken along 'line 2-2 of that figure.

FIGURE 3 is a cross-sectional view of one preferred form of theinvention showing a carbon brush having a cylindrical cavity.

FIGURE 4 is a cross-sectional view of the brush assembly shown in FIGURE3, and is taken along line 4-4 of that figure, looking in the directionof the arrows.

FIGURE 5 is a cross-sectional view of an alternate form of brush havinga frusto-conical cavity for holding one end of the spring.

FIGURE 6 is a cross-sectional View of another alternate form of brushalso having a frusto-conical cavity with the cone reversed.

FIGURE 7 illustrates another form of the invention in which the cavityis ring-shaped.

FIGURE 8 illustrates another form of the invention employing a dovetailslot in the top of the brush.

FIGURE 9 is a view similar to FIGURE 3 in which the cavity is internallythreaded to anchor the spring.

FIGURE 10 is a view similar to FIGURE 5 in which the cavity isinternally threaded.

FIGURE 11 is a cross-sectional view taken on line 11-11, in FIGURE 8.

Referring to FIGURES 1 and 2, a prior art brush assembly is shown forcomparison. A hollow, generally rectangular brush holder 10 is formedwith a brush receiving central portion 11. A brush 12A is slidablycarried within the holder 10 and rides upon a commutator 13. The upperend of brush 12A is formed with a cylindrical stub 14 which helps toposition the lower end of a helical spring 15. The upper end of spring15 may be supported by a washer 16 although there are other structureswhich 3 may be used for this purpose. The washer 16 is held against acap 17 which closes the upper end of the brush holder 10 and is securedto it by screw threads.

The electrical junction-s between the spring ends and the brush and capare not sufficient to provide a good low resistance path. Also, if thespring is of steel it cannot pass currents greater than one-quarteramperes with any efficiency. For this reason, a flexible copper wireshunt 18 is connected between the upper end 14 of the brush 12A andwasher 16 to carry all of the current. This type of construction iscostly but necessary when steel springs are used.

One form of the present invention is shown in FIG- URES 3 and 4. In thisform, the top of the brush 12B contains a cavity 21, instead of having astub and the exterior flat faces of the brush which make sliding contactwith the inside surfaces 11 of holder 10 have a greater bearing lengthand are lesssubject to binding due to tilting particularly as the brush.gets smaller. The lower end of spring 15 is compactly wound in a smallhelix which is tightly fitted into cavity 21. The upper end of thespring 15 bears against the bottom Olf cap 17A, which urges it againstthe brush 1213. This type of connection at the brush end is well suitedto a spring under compressive tension because, as is well known, thecoils of a helical spring expand when the spring is compressed. When cap17A is screwed into place the lower end of the spring tends to expandand press tightly on the inner surfaces of the cavity 21, therebyproviding good electrical connections. If the spring is made ofberyllium copper or some of the other alloys, such as Cortem, theflexible shunt 18, shown in FIGURES 1 and 2, is not needed.

The brush 12D, shown in FIGURE 6, is still another alternate form of theinvention where the cavity is frustoconical but having its lowerdiameter smaller than the opening. As before, the lower end 200 ofspring 15 is formed to fit snugly into the cavity.

As a further embodiment of the present invention, the brush 12E shown inFIGURE 7, may be formed with a ring shaped cavity 22 to receive the endof the spring 15. The outside diameter of the core 23 within the ringshould be of a size which will provide a firm engagement with the spring15 and good electrical wiping contact.

tail slot 24 across the top of the brush 12F to receive the 'slid intothe groove laterally:

spring 15. In this form of the invention the spring may be In FIGURES 9and 10, the cavities 25, 26, are similar to those shown in FIGURES 3 and5 except they are internally threaded as indicated at 27, 28, to receivethe spring 15. The threads have a pitch and depth to accommodate thespring size and helix.

While this brush assembly has been designed primarily for small motorsusing cylindrical shaped commutators or slip rings, it is obvious thatthey may be used in any brush assembly which makes sliding contact witha moving conductive surface.

Having thus fully described the invention, What is claimed as new anddesired to be secured by Letters Patent of the United States, is:

1. A carbon brush assembly for electrical motors which include acylindrical revolving axially aligned conductor comprising, a carbonbrush rod having a substantially constant cross sectional shape, a brushholder having a hollow portion for slidably retaining the brush, saidbrush being formed with a cylindrical cavity at one end, a helicalspring for resiliently holding the other end of the brush against saidrevolving conductor, one end of said spring having a helical end portionof reduced diameter and a shape similar to the brushcavity which end ispositioned in said brush cavity for making electrical contact with thesides of the cavity, and a conductive cap secured to said holder formaking an electrical connection to the other end of the spring.

2. A carbon brush assembly as claimed in claim 1 wherein the cavity isring shaped in cross section.

References Cited UNITED STATES PATENTS 626,708 6/ 1899 Lundell 310 -249XR 1,743,682 l/1930 Oswald 310-248 XR 2,199,532 5/1940 Weeks 310-2492,615,939 10/ 1952 Mitchell 310249 XR FOREIGN PATENTS 1,039,415 8/ 1966Great Britain.

651,170 10/ 1937 Germany.

The embodiment shown in FIGURE 8 employs a dove- 45 MILTON HIRSHFIELDPrimary Examiner D. F. DUGGAN, G. NUNEZ, Assistant Examiners.

